At the end of the day, I would like my MacBook Pro to back-up to both Time Machine and Backblaze (or verify that it has done so) and then shut down. Could someone write please write a script that would implement this? Thank you.
I don't know about Backblaze, but one option would be to edit the crontab with
EDITOR=nano crontab -e and add a line like this:
0 18 * * * tmutil startbackup -b && osascript -e 'tell app "System Events" to shut down'